This is a proposal from a group of five NIH funded neuroscientists interested in understanding how the structural and functional organization of the brain arises during development and changes with experience. Because these studies examine the nervous system at the level of individual cells and their processes, they are particularly amenable to the techniques of modern optical microscopy. We are requesting funds to purchase a newly available commercial two-photon/confocal microscope system that will permit high-resolution optical images of neural preparations.For each of the proposed projects, we have found that more traditional imaging approaches has limited capabilities. Four of the five proposals center of imaging living nerve cells over time either in intact animals or in explanted neural preparations. The fifth involves thick specimens of literally priceless human tissue. Studies include the time- lapse observation of the development of GFP labeled synaptic circuits in C. elegans, following the development of axonal projects in the vertebrate optic tectum, monitoring synaptic competition at the neuromuscular junction, assaying functional alterations in the developing retina and describing changes in cortical circuitry in aging human brain samples. The range of questions and preparations being used assures that this system will provide valuable new information for many different kinds of neuroscience studies. Our microscope system will be housed in the Bakewell Neuroimaging Laboratory a shared facility immediately adjacent to three of the five main users' laboratories and near the other two investigators' labs. The device will have long-term institutional support from a special endowment to the NeuroImaging laboratory. The device will have long-term institutional support from a special endowment to the NeuroImaging laboratory. The device will be available to other members of the neuroscience community at Washington University as time permits.